Actually the other two options for Warlock master also dont sound pleasant.
About Wizard, I would assume that the spells you "instantly" learn at levelup would actually be spells you have researched on your own time before the levelup.
Either way the solution that we get to learn two spells at levelup is purely from the gaming experience just so much better than the solution in AD&D, when there was a good chance that you would levelup, especially on the lower levels in BG1, and you would simply not know any spell on that new spell level, and there was also no upcasting back in AD&D either, so these slots have been completely useless to you.
